add (host options): add basic host options

options/host/xserver.nix

@@ -0,0 +1,25 @@
+{ lib, config, ... }:
+let
+  cfg = config.host.xserver;
+in
+{
+  options = {
+    host.xserver = {
+      enable = lib.mkOption {
+        types = lib.types.bool;
+        default = true;
+        description = "Xserver configurations for host.";
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.xserver = {
+      enable = true;
+      xkb = {
+        layout = "us";
+        variant = "";
+      };
+    };
+  };
+}